Genetic manipulation of mouse models has been an extremely productive approach to studying basic biological mechanisms. A Genetics Core has been established and has been productive during the last funding period. The RDCC proposes to continue support of the Genetics Core to provide two major services: 1) Transgenic and knockout mouse production and 2) Speed congenics. The transgenic and knockout mouse production facility provides additional services including blastocyst complementation, derivation of new embryonic stem cell lines, cryopreservation, and mouse embryonic fibroblast production. The speed congenics facility provides genome wide typing for the purposes of enhancing backcrossing of mice into defined genetic backgrounds. Thus, the facility will enhance the study of basic mechanisms underlying rheumatic diseases.